This project is designed to test the hypothesis that Ca++ plays an important role as a messenger in coordinating the rate of substrate metabolism with the rate of mechanical power utilized by the heart. While this hypothesis is not new (12,96), most previous studies have not tested this in the intact tissue. However, recent studies performed here on rabbit papillary muscles suggest that: 1. Ca++ from different intracellular pools can affect the dynamic relation between metabolism and contractile function; 2. the three major metabolic pathways (glycolysis, Beta oxidation and TCA) are not equally sensitive to regulation by Ca++ and 3. The source of the Ca++ is important. This project will continue these studies and in particular seek answers to the following three questions: 1. What is the relative contribution to this messenger pool of Ca++ originating from the slow channels, glycocalyx and the SR; 2. what are the effects of the separate sources of Ca++ on the different metabolic pathways; and finally, 3. do endogenous catecholamines contribute to these metabolic effects? To assess metabolic response to changes in mechanical power dissipation, the change in the redox state of the pyridine nucleotides (PN) will be noninvasively measured using a microfluorometer. The ratio of the change in redox state of the PN produced per unit change in mechanical power, defined as the coupling coefficient, will be used as a measure of metabolic sensitivity in the rabbit papillary muscle. To determine the relative contribution of the different Ca++ sources to the messenger pool, the effect of different agents on the coupling coefficient will be determined. Specifically, nifedipine, verapamil and angiotensin will be used to affect the slow channels; and ryanodine and methylxanthines the SR. Appropriate agonists and antagonists will be used to determine the contribution of catecholamines. The sensitivity of the different metabolic pathways will be determined by comparing the effect of these agents on the coupling coefficient in the presence of different substrates (glucose, butyrate and pyruvate). Experiments on isolated mitochondria will also be performed to determine whether, and if so to what extent, Ca++ associated with the membrane/matrix modulates metabolic function. This project will provide valuable new information about an essential regulatory process of the intact myocardium.